A valve timing control apparatus is known in the art for controlling a valve opening and/or closing timing of an intake valve and/or an exhaust valve of an engine. The valve timing control apparatus has advancing oil chambers and retarding oil chambers between a vane rotor and a housing, wherein the vane rotor is movable relative to the housing. Fluid pressure of working fluid, which is supplied into the respect advancing and retarding oil chambers, is controlled so as to control a rotational phase between the vane rotor and the housing.
According to the above conventional valve timing control apparatus, an operational mode for supplying the working fluid from an oil pump to the advancing oil chambers is changed to another operational mode for supplying the working fluid from the oil pump to the retarding oil chambers, or vice versa, so as to control the fluid pressure in the advancing and retarding oil chambers. The relative rotational position of the vane rotor to the housing is changed by such fluid pressure control, to thereby realize the control of the valve opening and/or closing timing.
It is also known in the art to provide an elastic member in the valve timing control apparatus in order to improve response of the operation, in which the elastic member biases the vane rotor to rotate in an advancing or retarding direction with respect to the housing.
In addition, it is known in the art, for example, as disclosed in Japanese Patent No. 4084585, to provide a signal rotor fixed to a vane rotor so that the signal rotor rotates together with the vane rotor. A sensor is provided at an outer peripheral side of the signal rotor to detect a rotational angle of a driving shaft or a driven shaft, with which the vane rotor rotates together.
In the case that the signal rotor and the elastic member are provided on the same side in an axial direction, that is, on a front side of the valve timing control apparatus, a sensor for detecting the rotational angle of the signal rotor may misidentify the elastic member (including a fixing member for fixing an end of the elastic member to the signal rotor) as a portion of the signal rotor. It may be, therefore, difficult to exactly detect the rotational angle of the signal rotor, which is fixed to the driving shaft or the driven shaft.